/*
 * Copyright 2002-2019 the original author or authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      https://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.springframework.lang;

import java.lang.annotation.Documented;
import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;

import javax.annotation.Nonnull;
import javax.annotation.meta.TypeQualifierNickname;

/**
 * 一个常见的Spring注解，声明注解的元素不能是{@code null}。
 *
 * 利用JSR-305元注释来表明Java中的无效性，使之成为常见的支持JSR-305的工具，并由Kotlin用于推断Spring API的无效性。
 *
 * 应该在参数、返回值和字段级别使用。
 * 方法重写应该重复父级{@code @NonNull}注释，除非它们的行为不同。
 *
 * 使用 {@code @NonNullApi} (scope = parameters + return values) 和/或 {@code @NonNullFields} * (scope = fields)
 * (scope = fields)来设置默认行为为non-nullable，以避免在你的整个代码库中注解你的整个代码库都有{@code @NonNull}。
 *
 * @author Sebastien Deleuze
 * @author Juergen Hoeller
 * @since 5.0
 * @see NonNullApi
 * @see NonNullFields
 * @see Nullable
 */
@Target({ElementType.METHOD, ElementType.PARAMETER, ElementType.FIELD})
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Nonnull
@TypeQualifierNickname
public @interface NonNull {
}
